Small diameter glass fibers are useful in a variety of applications the most important of which is as acoustical or thermal insulation materials. When these small diameter glass fibers are properly assembled into a lattice or web, commonly called a wool pack, fibers which individually lack strength or stiffness can be formed into a product which is quite strong. The glass fiber insulation material which is produced is lightweight, highly compressible and resilient.
The common prior art methods for producing glass fiber wools involve forming wool batts using primarily straight glass fibers and then compressing these batts into packages for shipping. Unfortunately, glass fiber products currently produced have several common problems. First, during their attenuation, the individual, primarily straight fibers tend to align themselves with each other to form rope-like structures. These structures lead to local variation in wool pack fiber density, decreasing the insulating value of the material. Second, it is necessary to use some material, commonly a phenol-formaldehyde resin, to bind the fibers together. Last, under sufficiently high compression, fiber fracture reduces the ability of the wool batt to recover to its designed thickness. Thus, there is a need for an improved glass fiber product which will withstand greater compression and provide greater entanglement of the fibers within the product. Also, it is desirable to provide a more uniform, less ropey fiber structure in the insulation product.
Attempts have been made in the prior art to produce curly glass fibers for use as staple fibers and to produce glass fiber mats with high entanglement. Stalego in U.S. Pat. No. 2,998,620 discloses helical curly glass fibers of bicomponent glass compositions. Stalego teaches producing curly fibers by passing two glass compositions of differing degrees of thermal expansivity through the orifices of a spinner. The glasses are extruded in aligned integral relationship such that the fibers curl naturally upon cooling due to the differing thermal expansivity.
However, the glass compositions disclosed by Stalego are not suitable for rotary forming technology. For example, in the glass pairs Stalego discloses, E glass is the low thermal expansion glass. In order for a glass to form satisfactorily in the rotary process, the glass must enter the spinner at temperatures close to that at which it has a viscosity of 1000 poise. At this viscosity E glass has a temperature near 2190.degree. F. (1200.degree. C.) which is high enough to cause rapid damage to the metals from which the spinners are made. This effectively prohibits the use of E glass for the extended periods necessary for commercial production. To varying degrees, similar problems exist with all of the high thermal expansion glasses disclosed by Stalego.
Tiede in U.S. Pat. No. 3,073,005 discloses a nonrotary process for making bicomponent curly glass fibers. The fibers are made by feeding differing glass compositions to an orifice in side by side contact such that the two glasses are attenuated into a single fiber. Since Tiede discloses the same glass composition as Stalego, he does not disclose glass compositions useful for commercial production of glass fiber products by the rotary process.
Accordingly, a need exists for improved glass compositions useful for producing glass fibers that would exhibit improved recovery and thermal conductivity when produced by the rotary process.